A highly selective, sensitive, rapid and economical differential pulse polarographic method has been developed for the determination of trace amount of cadmium in various standard alloys and biological samples after adsorption of its 2-nitroso-1-naphthol-4-sulplionic acid - tetradecyldimethylbenzylammonium chloride on microcrystalline naphthalene in the pH range of 5.7-11.0. After filtration, the solid mass is shaken with 9.0 mL of 1 M hydrochloric acid and cadmium is determined by differential pulse polarography (DPP). Cadmium can alternatively be adsorbed on 2-nitroso-1-naphthol-4-sulphonic acid-tetradecyldimetliylbenzylammonium-naphthalene adsorbent packed in a column and determined. In this case, 0.9 mug of cadmium can be concentrated in a column from 300 mL of aqueous sample, where its concentration is as low as 3 ng/mL. Characterization of the electroactive process included an examination of the degree of reversibility. Various parameters such as the effect of pH, volume of aqueous phase, HCl concentration, reagent concentration, naphthalene concentration, shaking time and interference of a number of metal ions on the determination of cadmium have been studied in detail to optimize the conditions for determination in standard alloys and standard biological samples.